Technologies are generally described for monitoring application health in datacenters through load rebalancing. In some examples, a domain name server (DNS) module may cyclically vary load provided to an application instance. A monitoring module may then measure application output data and/or parameters associated with the processing of the load by the application based on a difference or a comparison between parts of the cyclical load variation. The monitoring module may use the measured data/parameters to both determine the health of the application instance and to cause the DNS module to adjust the periodic variation of the load.